Imaging apparatus and analyzing apparatus

ABSTRACT

An imaging apparatus includes a lens optical system including a lens, a stop, and first through nth divided optical elements in which first through nth optical regions are defined, respectively, along a plane perpendicular to an optical axis and positioned to be point-symmetric with respect to the optical axis, an image sensor, and a microlens array guiding light that has passed through the first through nth optical regions to the first through nth pixels of the image sensor, respectively. At least three of s 1 , . . . , and S n  are mutually different and a relation of s i ≧s i+1  is satisfied, where s 1 , . . . , and s n  represent mean luminances of images obtained from the first through nth pixels, respectively. The first optical region and the nth optical region are positioned not to be point-symmetric to each other with respect to the optical axis.

BACKGROUND

1. Technical Field

The present disclosure relates to imaging apparatuses, such as cameras,and to analyzing apparatuses that include cameras or the like.

2. Description of the Related Art

Apparatuses that capture images with different optical characteristics(e.g., wavelength, polarization, exposure) by a single imaging systemthrough a single instance of imaging are proposed. The specification ofJapanese Patent No. 5001471 discloses an embodiment of such an imagingapparatus. In this apparatus, divided regions are provided in thevicinity of a stop of a lens optical system, and elements with mutuallydifferent optical characteristics are disposed in the respectiveregions. A microlens array is disposed between the lens optical systemand an image sensor, and light rays that have passed through thedifferent elements in the vicinity of the stop are incident on differentpixels on the image sensor.

SUMMARY

In one general aspect, the techniques disclosed here feature an imagingapparatus that includes a lens optical system, an image sensor, and amicrolens array. The lens optical system includes a lens, a stop, and anoptical element including first through nth divided optical elements andhaving first through nth optical regions, and n is an integer equal toor greater than five. The first through nth optical regions are definedin the respective first through nth divided optical elements along aplane perpendicular to an optical axis and positioned to bepoint-symmetric with respect to the optical axis. Light that has passedthrough the first through nth optical regions is incident on the imagesensor including first through nth pixels. The microlens array isdisposed between the lens optical system and the image sensor. Themicrolens array guides the light that has passed through the firstthrough nth optical regions to the first through nth pixels,respectively; and mean luminances of images obtained from the firstthrough nth pixels when a predetermined object is imaged under apredetermined illumination condition by using the lens optical system,the image sensor, and the microlens array are represented by s₁, s₂, . .. , and s_(n), respectively. At least three of s₁, s₂, . . . , and s_(n)are mutually different values, and a relation of s_(i)≧s_(i+1) issatisfied for any i that satisfies 1≦i≦n−1. The first optical region andthe nth optical region are positioned not to be point-symmetric to eachother with respect to the optical axis.

One non-limiting and exemplary embodiment provides an imaging apparatusthat can obtain images with different optical characteristics withhigher accuracy. In addition, a more accurate analytical value ofcharacteristics of an object can be obtained.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a configuration of an imagingapparatus according to a first embodiment;

FIG. 2A is a front view of regions according to the first embodiment ofthe present disclosure;

FIG. 2B is a front view of an optical element according to the firstembodiment of the present disclosure;

FIG. 3 is an enlarged view of a microlens array and an image sensoraccording to the first embodiment;

FIG. 4 is an enlarged sectional view of the microlens array and theimage sensor according to the first embodiment;

FIG. 5 is a flowchart for describing a method for determining anarrangement of divided optical elements according to the firstembodiment;

FIG. 6 illustrates an arrangement of divided optical elements heldbefore the arrangement of the divided optical elements is determinedaccording to the first embodiment;

FIG. 7 illustrates an arrangement of divided optical elements accordingto the first embodiment;

FIG. 8 illustrates a conventional arrangement of divided opticalelements according to a comparative example;

FIG. 9 is a front view of regions according to a second embodiment;

FIG. 10 is a flowchart for describing a method for determining anarrangement of divided optical elements according to the secondembodiment;

FIG. 11 illustrates an arrangement of divided optical elements heldbefore the arrangement of the divided optical elements is determinedaccording to the second embodiment;

FIG. 12A illustrates an arrangement of divided optical elementsaccording to another embodiment;

FIG. 12B illustrates an arrangement of divided optical elementsaccording to yet another embodiment;

FIG. 12C illustrates an arrangement of divided optical elementsaccording to yet another embodiment;

FIG. 13A illustrates an arrangement of divided optical elementsaccording to yet another embodiment;

FIG. 13B illustrates an arrangement of divided optical elementsaccording to yet another embodiment;

FIG. 14 illustrates a configuration of a conventional imaging apparatusand a light ray therein;

FIG. 15 illustrates a position on an optical element through which alight ray passes in the conventional imaging apparatus;

FIG. 16 illustrates positions on an image sensor on which light rays areincident in the conventional imaging apparatus;

FIG. 17A illustrates images captured by the conventional imagingapparatus; and

FIG. 17B illustrates normal images in the transmission wavelength bandof each band-pass filter in the conventional imaging apparatus.

DETAILED DESCRIPTION Underlying Knowledge Forming Basis of the PresentDisclosure

The inventor of the present disclosure has studied the details of theconventional imaging apparatus disclosed in the specification ofJapanese Patent No. 5001471, and has found a problem that a ghost imagein a second wavelength band is mixed into an image in a first wavelengthband and a ghost image in the first wavelength band is mixed into animage in the second wavelength band. Even when the number of regions(i.e., the types of band-pass filters) is increased to more than two,the mixing of a ghost image occurs.

In addition, the inventor has found a problem that, since images withdifferent optical characteristics are mixed, even if the characteristicsof an object are analyzed by using these images, the accuracy of ananalytical value is insufficient. In view of such problems, the inventorof the present disclosure has inquired into what causes a ghost image tobe mixed into another image, and has conceived of a novel imagingapparatus that can suppress an influence of a ghost image and obtain anaccurate analytical value of an object. An overview of an aspect of thepresent disclosure is as follows.

An imaging apparatus according to one aspect of the present disclosureincludes

a lens optical system including

-   -   a lens,    -   a stop, and    -   an optical element including first through nth divided optical        elements and having first through nth optical regions, n being        an integer equal to or greater than five, the first through nth        optical regions being defined in the respective first through        nth divided optical elements along a plane perpendicular to an        optical axis and positioned to be point-symmetric with respect        to the optical axis;

an image sensor on which light that has passed through the first throughnth optical regions is incident, the image sensor including firstthrough nth pixels; and

a microlens array disposed between the lens optical system and the imagesensor, the microlens array guiding the light that has passed throughthe first through nth optical regions to the first through nth pixels,respectively,

wherein mean luminances of images obtained from the first through nthpixels when a predetermined object is imaged under a predeterminedillumination condition by using the lens optical system, the imagesensor, and the microlens array are represented by s₁, s₂, . . . , ands_(n), respectively,

at least three of s₁, s₂, . . . , and s_(n) are mutually differentvalues,

a relation of s₁≧s_(i+1) is satisfied for any i that satisfies 1≦i≦n−1,and

the first optical region and the nth optical region are positioned notto be point-symmetric to each other with respect to the optical axis.

In the present disclosure, the first through nth optical regions arereferred to as optical regions AF₁, AF₂, . . . , and AF_(n), and thefirst through nth pixels are referred to as pixels f₁, pixels f₂, . . ., and pixels f_(n). The first through nth optical regions may be definedby the stop in the respective first through nth divided opticalelements.

An imaging apparatus according to another aspect of the presentdisclosure includes

a lens optical system including

-   -   a lens,    -   a stop, and    -   an optical element including first through nth divided optical        elements and having first through nth optical regions, n being        an integer equal to or greater than five, the first through nth        optical regions being defined in the respective first through        nth divided optical elements along a plane perpendicular to an        optical axis and positioned to be point-symmetric with respect        to the optical axis;

an image sensor on which light that has passed through the first throughnth optical regions is incident, the image sensor including firstthrough nth pixels; and

a microlens array disposed between the lens optical system and the imagesensor, the microlens array guiding the light that has passed throughthe first through nth optical regions to the first through nth pixels,respectively,

wherein areas of the first through nth optical regions are representedby D₁, D₂, . . . , and D_(n), respectively,

transmittances of the first through nth optical regions under apredetermined illumination condition are represented by T₁, T₂, . . . ,and T_(n), respectively,

sensitivities in the first through nth pixels when the light that haspassed through the first through nth optical regions are incident on thefirst through nth pixels are represented by R₁, R₂, . . . , and R_(n),respectively, andB _(m) =D _(m) ×T _(m) ×R _(m) (m=1 through n),

at least three of B₁, B₂, . . . , and B_(n) are mutually differentvalues,

a relation of B_(i)≧B_(i+1) is satisfied for any i that satisfies1≦i≦n−1, and

the first optical region and the nth optical region are positioned notto be point-symmetric to each other with respect to the optical axis.

In the imaging apparatus according to the one aspect of the presentdisclosure, at least two of areas of the first through nth opticalregion may be different from each other.

In the imaging apparatus according to the other aspect of the presentdisclosure, at least two of areas of the first through nth opticalregions may be different from each other.

In the imaging apparatus according to the one aspect of the presentdisclosure, at least two of the sensitivities in the first through nthpixels when the light that has passed through the first through nthoptical regions are incident on the first through nth pixels may bedifferent from each other.

In the imaging apparatus according to the other aspect of the presentdisclosure, at least two of R₁, R₂, R₃, and R₄ may be different fromeach other.

The predetermined object may be a white reflectance standard.

The (n−1)th optical region and the nth optical region may be positionedto be point-symmetric to each other with respect to the optical axis.

The first optical region and the second optical region may be positionedto be point-symmetric to each other with respect to the optical axis.

The first optical region and the nth optical region may not be adjacentto each other.

The predetermined illumination condition may be a condition in whichlight is emitted from a halogen lamp.

At least one of the first through nth divided optical elements may be aband-pass filter.

A center of a transmission wavelength band of the band-pass filter maylie in a range from 700 nm to 1100 nm inclusive.

At least one of the first through nth divided optical elements may be apolarization filter.

At least one of the first through nth divided optical elements may be aneutral density (ND) filter.

An analyzing apparatus according to an aspect of the present disclosuremay include any one of the imaging apparatuses described above, and aprocessor adapted to obtain an analytical value of the object on thebasis of images that are obtained from the first through nth pixels.

The imaging apparatus that the inventor of the present disclosure hasconceived of is based on the result obtained by investigating whatcauses a ghost image to appear. With reference to FIGS. 14 through 17B,the cause will be described, hereinafter.

FIG. 14 illustrates an example of a light ray in the conventionalimaging apparatus. According to the apparatus disclosed in thespecification of Japanese Patent No. 5001471, a light ray R_(λ1) at awavelength of λ₁ passes through a point X on a band-pass filter F_(λ1)(whose transmission wavelength is the wavelength λ₁) and is converged bya lens L₁. Then, the light ray R_(λ1) reaches a point Y on an imagesensor N through a microlens array K and is incident on a pixelcorresponding to the band-pass filter F_(λ1).

At this point, part of the light ray R_(λ1) is reflected by the surfaceof the image sensor N. This reflected light ray passes through themicrolens array K and the lens L₁ and reaches a point X′ on a band-passfilter F_(λ2). When the transmission wavelength band of the band-passfilter F_(λ2) does not include the wavelength λ₁, part of the light rayR_(λ1) is reflected by the surface of the band-pass filter F_(λ2) and isconverged by the lens L₁. Then, this part of the light ray R_(λ1)reaches a point Y′ on the image sensor N through the microlens array Kand is incident on a pixel corresponding to the band-pass filter F_(λ2).As a result, a ghost image in a first wavelength band is mixed into animage in a second wavelength band.

In the meantime, when a light ray at a wavelength λ₂ is incident on theband-pass filter F_(λ2) (whose transmission wavelength is the wavelengthλ₂), a ghost image in the second wavelength band is mixed into an imagein the first wavelength band.

FIG. 15 illustrates a position through which the light ray R_(λ1)passes, as viewed so as to face the band-pass filters F_(λ1) and F_(λ2).As illustrated in FIG. 15, the points X and X′ are located so as to bepoint-symmetric with respect to an optical axis V₀. Thus, it isunderstood that optical elements (i.e., band-pass filters) that aredisposed so as to be point-symmetric with respect to the optical axis V₀contribute to the appearance of ghost images in their respective images.

FIG. 16 illustrates positions on which the light ray R_(λ1) is incident,as viewed so as to face the image sensor N. As illustrated in FIG. 16,the points Y and Y′ are located so as to be point-symmetric with respectto the optical axis V₀. Thus, it is understood that, when the center ofthe image sensor N coincides with the optical axis V₀, ghost imagesappear as images that are point-symmetric with respect to the center ofthe image.

FIG. 17A illustrates an example of images obtained by the conventionalimaging apparatus, and FIG. 17B illustrates normal images for thetransmission wavelength band of each band-pass filter in theconventional imaging apparatus. If there is no light ray that isreflected by the surface of the image sensor, only the normal imagescorresponding to the respective transmission wavelength bands can becaptured, as illustrated in FIG. 17B. However, in reality, asillustrated in FIG. 17A, there is a problem in that a ghost image ismixed into an image due to the reflection by the surface of the imagesensor and the reflection by optical elements disposed so as to bepoint-symmetric with respect to the optical axis.

The imaging apparatus according to the present disclosure solves theproblem of the conventional imaging apparatus described above, andsuppresses an influence of a ghost image, making it possible to obtainan accurate analytical value of an object.

Hereinafter, with reference to the drawings, embodiments of the imagingapparatus will be described in specific terms.

First Embodiment

FIG. 1 illustrates a configuration of an imaging apparatus according toa first embodiment of the present disclosure. The imaging apparatusaccording to the present embodiment includes a lens optical system Lhaving an optical axis V₀, a microlens array K disposed in the vicinityof a focal point position of the lens optical system L, and an imagesensor N.

In the present embodiment, the lens optical system L includes a stop Sand an objective lens L₁ that images light that has passed through thestop S on the image sensor N. A region A is disposed in the vicinity ofthe stop S and along a plane perpendicular to the optical axis V₀. Thesize of the region A is substantially the same as the size of the stop Sand is, for example, circular in shape.

The lens optical system L further includes an optical element F disposedin the region A.

FIG. 2A is a front view of the region A. As illustrated in FIG. 2A, theregion A is divided into six regions A₁ through A₆. The regions A₁through A₆ are disposed so as to be point-symmetric with respect to theoptical axis V₀.

FIG. 2B is a front view of the optical element F. The optical element Fis divided into portions that are shaped so as to correspond to theshapes of the respective regions A₁ through A₆. In other words, theoptical element F includes six divided optical elements. Of the sixdivided optical elements, at least three divided optical elements havemutually different optical characteristics. Each of the divided opticalelements has substantially uniform optical characteristics. Asillustrated in FIGS. 1 and 2B, the size of the optical element F may begreater than the size of the region A (i.e., part of the optical elementF overlaps the stop S).

In the present embodiment, the optical element F has mutually differenttransmission wavelength band characteristics in the regions A₁ throughA₆. To be more specific, the divided optical elements located in therespective regions A₁ through A₆ are band-pass filters with mutuallydifferent transmission wavelength bands. The divided optical elementsmay be polarization filters or neutral density (ND) filters. In otherwords, the optical characteristics being different means that at leastone selected from the group of the transmission wavelength band, thepolarization characteristics, and the transmittance differs among theregions A₁ through A₆.

A band-pass filter obtained, for example, by depositing a dielectricmultilayer film on an optical glass substrate can be used. The band-passfilters with different optical characteristics may be fabricated, forexample, through a method in which dielectric multilayer films withdifferent constitutions are deposited on substrates shaped so as tocorrespond to the shapes of the respective regions (sector shape in thepresent embodiment) and the substrates are then arranged to form acircle. Regardless of a fabrication method, the optical characteristicsof portions near the boundaries of the regions are likely to falloutside the desired optical characteristics, and thus the portions nearthe boundaries of the regions A₁ through A₆ may be covered bylight-blocking zones.

Light rays R that enter the stop S pass through any one of the regionsA₁ through A₆ (i.e., the optical element F) illustrated in FIG. 2A andis converged by the lens L₁. Then, the light rays R pass through themicrolens array K and are incident on the image sensor N.

FIG. 3 is an enlarged view of the image sensor N, as viewed so as toface the image sensor N, and illustrates a positional relation betweenthe image sensor N and the microlens array K. The microlens array Kincludes micro-optical components M₁ each having a lens surface. Theimage sensor N includes pixels f₁, pixels f₂, pixels f₃, pixels f₄,pixels f₅, and pixels f₆. As illustrated in FIG. 3, the pixels f₆, f₄,and f₂ or the pixels f₅, f₃, and f₁ are arrayed periodically in thevertical direction of FIG. 3. In addition, the pixels f₆ and f₅, thepixels f₄ and f₃, or the pixels f₂ and f₁ are arrayed in an alternatingmanner in the horizontal direction of FIG. 3. In this manner, pixelsfrom the respective pixels f₁ through f₆ are disposed closely to form apixel group N₁. The pixel group N₁ corresponds to a single micro-opticalcomponent M₁ in the microlens array K.

FIG. 4 is an enlarged sectional view of the microlens array K and theimage sensor N illustrated in FIG. 1.

As illustrated in FIG. 4, in each micro-optical component M₁, of thelight rays R that have entered the stop S, large part of a light ray R₂that has passed through the region A₂ is incident on one of the pixelsf₂, large part of a light ray R₄ that has passed through the region A₄is incident on one of the pixels f₄, and large part of a light ray R₆that has passed through the region A₆ is incident on one of the pixelsf₆. In a similar manner, large part of light rays that have passedthrough the respective regions A₁, A₃, and A₅ are incident on acorresponding one of the pixels f₁, f₃, or f₅.

The image sensor N subjects the light rays incident on the pixels f₁through f₆ to photoelectric conversion, and transmits an image signal Qto a signal processor P, as illustrated in FIG. 1. The signal processorP generates an image Q₁ that is based on the pixels f₁ and an image Q₂that is based on the pixels f₂ on the basis of the image signal Q.Images Q₃ through Q₆ are also generated in a similar manner.

In this manner, the images that are based on the light rays that havepassed through the respective regions A₁ through A₆ can be obtained.Although the images Q₁ through Q₆ include parallaxes occurring due tothe differences among the positions of the regions A₁ through A₆, theimages Q₁ through Q₆ are substantially images obtained by imaging thesame object simultaneously. Imaging simultaneously as used herein meansthat the light rays for forming the images Q₁ through Q₆ are obtainedsimultaneously. The signal processor P does not need to generate theimages Q₁ through Q₆ simultaneously.

Although a mode in which six pixels from the respective pixels f₁through f₆ are disposed closely so as to form the pixel group N₁ isillustrated in the example described above, the configuration is notlimited thereto. For example, the pixel group N₁ may be formed by 6npixels (n is an integer equal to or greater than two). In this case, ineach micro-optical component M₁, of the light rays R that have enteredthe stop S, large part of the light ray R₂ that has passed through theregion A₂ is incident on the n pixels f₂, large part of the light ray R₄that has passed through the region A₄ is incident on the n pixels f₄,and large part of the light ray R₆ that has passed through the region A₆is incident on the n pixels f₆. In a similar manner, large part of thelight rays that have passed through the respective regions A₁, A₃, andA₅ are incident on the corresponding one of the n pixels f₁, f₃, and f₅.

Subsequently, a method for determining an arrangement of the dividedoptical elements in the regions A₁ through A₆ will be described withreference to the flowchart illustrated in FIG. 5.

The six divided optical elements are represented by F_(a), F_(b), F_(c),F_(d), F_(e), and F_(f). In a disposing step 501, the divided opticalelements F_(a) through F_(f) are disposed in the regions A₁ through A₆in the imaging apparatus, as illustrated in FIG. 6 (also refer to FIG.2A).

In an imaging step 502, a predetermined object is imaged by the imagingapparatus under a predetermined illumination condition, and the imagesQ₁ through Q₆ are obtained. An illumination with an optical spectrumthat is the same as the optical spectrum of an illumination in anenvironment in which the imaging apparatus is actually used may be usedas the predetermined illumination, which makes it possible to determinethe arrangement in the optical element F more accurately. In addition, ahalogen lamp may be used as the predetermined illumination. A halogenlamp has a relatively smooth optical spectrum from a visible light bandthrough a near-infrared band, and thus the halogen lamp offers anadvantage in that an analysis in these bands can be facilitated.

In addition, a white reflectance standard may be used as thepredetermined object. A white reflectance standard is a diffusereflector that has substantially uniform reflectance (e.g., 100%) acrossa wavelength band to be imaged. When a white reflectance standard isused, there is an advantage in that an influence of a ghost image isminimized on average when various objects with different spectralreflection characteristics, serving as actual targets of analysis, areimaged. It is to be noted that, when the spectral reflectancecharacteristics of actual targets of analysis are substantially thesame, the target of analysis may be used as the predetermined object inplace of the white reflectance standard.

In a calculation step 503, portions corresponding to the predeterminedobject are extracted from the obtained images Q₁ through Q₆, and a meanluminance of each of these portions is calculated. To calculate the meanluminance more accurately, a portion in which a ghost image overlaps maybe excluded from the portion corresponding to the predetermined object.

Alternatively, in order to prevent a ghost image from appearing, animage captured while regions other than the region corresponding to animage to be obtained are shielded may be used (e.g., when the image Q₁is to be obtained, the regions A₂, A₃, A₄, A₅, and A₆ are shielded).

After steps 501 through 503 are carried out, a relation between theregions A₁ through A₆ and the mean luminances of the images of thepredetermined object obtained from the light rays that have passedthrough the divided optical elements corresponding to the regions A₁through A₆ is obtained as indicated in Table 1. It is to be noted thatthe calculated values of the mean luminances indicated in Table 1 are anexample of the present embodiment.

TABLE 1 Calculated Divided Pixels Values of Mean Optical CorrespondingLuminances Regions Elements to Regions Images (Example) A₁ F_(a) f₁ Q₁100 A₂ F_(b) f₂ Q₂ 80 A₃ F_(c) f₃ Q₃ 60 A₄ F_(d) f₄ Q₄ 40 A₅ F_(e) f₅ Q₅30 A₆ F_(f) f₆ Q₆ 20

In a numbering step 504, the divided optical elements F_(a) throughF_(f) corresponding to the calculated mean luminances are rearranged andnumbered in descending order of the mean luminances. In other words,when the order of the mean luminances is expressed in symbols as ins₁>s₂>s₃>s₄>s₅>s₆, the corresponding divided optical elements arenumbered as in F₁, F₂, . . . , and F₆. Consequently, the divided opticalelements F_(a) through F_(f) can be numbered as the divided opticalelements F₁ through F₆, as indicated in Table 2.

TABLE 2 Mean Luminances Expressed in Symbols Numbered Divided Optical inDescending Order Divided Optical Regions Elements of Luminances ElementsA₁ F_(a) s₁ F₁ A₂ F_(b) s₂ F₂ A₃ F_(c) s₃ F₃ A₄ F_(d) s₄ F₄ A₅ F_(e) s₅F₅ A₆ F_(f) s₆ F₆

In a rearrangement step 505, the divided optical elements F₁ through F₆are rearranged in the regions A₁ through A₆ illustrated in FIG. 2A suchthat at least the divided optical element F₁ (i.e., divided opticalelement with the highest mean luminance) and the divided optical elementF₆ (i.e., divided optical element with the lowest mean luminance) aredisposed so as not to be point-symmetric with respect to the opticalaxis V₀. An example in which the divided optical elements F₁ through F₆have been rearranged is illustrated in FIG. 7. The regions A₁ through A₆in which the divided optical elements F₁ through F₆ have been rearrangedare referred to, respectively, as optical regions AF₁ through AF₆, whichhave optical characteristics of the divided optical elements F₁ throughF₆. When the light rays that have passed through the optical regions AF₁through AF₆ are incident on the respective pixels f₁ through f₆; thedivided optical elements rearranged in the regions A₁ through A₆, theoptical regions AF₁ through AF₆, the corresponding pixels, and the meanluminances represented by the symbols hold a relation as indicated inTable 3. In this case, the pixels f₁ through f₆ correspond to the pixelsf₁, f₆, f₄, f₃, f₂, and f₅ in each pixel group illustrated in FIG. 3.

TABLE 3 Rearranged Pixels Mean Luminances Divided CorrespondingExpressed in Symbols Optical Optical to Optical in Descending OrderRegions Elements Regions Regions of Luminances A₁ F₁ AF₁ f₁ s₁ A₂ F₅ AF₅f₅ s₅ A₃ F₄ AF₄ f₄ s₄ A₄ F₃ AF₃ f₃ s₃ A₅ F₆ AF₆ f₆ s₆ A₆ F₂ AF₂ f₂ s₂

As described thus far, the configuration of the imaging apparatusaccording to the present embodiment is such that an optical region inwhich a light ray is incident on pixels from which an image with thehighest mean luminance can be obtained when the divided optical elementsare disposed so as to be point-symmetric with respect to the opticalaxis and a predetermined object is imaged under a predeterminedillumination condition and another optical region in which a light rayis incident on pixels from which an image with the lowest mean luminancecan be obtained when the divided optical elements are disposed so as tobe point-symmetric with respect to the optical axis and thepredetermined object is imaged under the predetermined illuminationcondition are disposed so as not to be point-symmetric with respect tothe optical axis. FIG. 7 illustrates an example of such an arrangementof the divided optical elements and the optical regions.

Subsequently, the extent by which an influence of a ghost image can bereduced by rearranging the divided optical elements as described abovewill be described on the basis of a calculation.

As a conventional comparative example, an arrangement of divided opticalelements as illustrated in FIG. 8 (i.e., an arrangement of dividedoptical elements before the divided optical elements are rearranged inthe present embodiment) is given. In this comparative example, thedivided optical element F₁ in which the highest mean luminance isobtained when the predetermined object is imaged under the predeterminedillumination condition and the divided optical element F₆ in which thelowest mean luminance is obtained are disposed so as to bepoint-symmetric.

For now, suppose that certain divided optical elements F_(α) and F_(β)(α and β are integers that are each equal to or greater than 1 and equalto or less than the number of regions) are disposed so as to bepoint-symmetric with respect to the optical axis, with the mixing ofghost images into each other occurring due to these divided opticalelements taken into consideration, the mixing rate of a ghost image isdefined by (the mean luminance of a ghost image÷the mean luminance of anormal image). The quantity of light that is incident on the imagesensor N after having passed through the divided optical element F_(α)isrepresented by P_(α); the quantity of light that is incident on theimage sensor N after having passed through the divided optical elementF_(β) is represented by P_(β); the sensitivity of the image sensor N tothe light that has passed through the divided optical element F_(α) isrepresented by R_(α); and the sensitivity of the image sensor N to thelight that has passed through the divided optical element F_(β) isrepresented by R_(β). In this case, the mixing rate Mx(F_(α),F_(β)) of aghost image in an image corresponding to the divided optical elementF_(α) is expressed as follows.

$\begin{matrix}{{{Mx}\left( {F_{\alpha},F_{\beta}} \right)} = \frac{P_{\beta} \times C \times R_{\beta}}{P_{\alpha} \times R_{\alpha}}} & (1)\end{matrix}$Here, C represents an occurrence rate of a ghost image (i.e., thereflectance of the surface of the image sensor×the reflectance of theoptical element).

The mean luminance of a normal image in an image corresponding to thedivided optical element F_(α) is represented by s_(α), and the meanluminance of a normal image in an image corresponding to the dividedoptical element F_(β) is represented by s_(β). In this case, theluminance of an image can be expressed by a product of the quantity oflight and the sensitivity, and thus Mx(F_(α),F_(β)) in Expression 1 canbe expressed as in the following expression.

$\begin{matrix}{{{Mx}\left( {F_{\alpha},F_{\beta}} \right)} = \frac{s_{\beta} \times C}{s_{\alpha}}} & (2)\end{matrix}$In a similar manner, the mixing rate Mx(F_(β),F_(α)) of a ghost image inan image corresponding to the divided optical element F_(β) is expressedas follows.

$\begin{matrix}{{{Mx}\left( {F_{\beta},F_{\alpha}} \right)} = {\frac{P_{\alpha} \times C \times R_{\alpha}}{P_{\beta} \times R_{\beta}} = \frac{s_{\alpha} \times C}{s_{\beta}}}} & (3)\end{matrix}$

Table 4 indicates a result obtained by calculating the mixing rate of aghost image arising in the arrangement of the divided optical elementsaccording to the present embodiment (i.e., the arrangement illustratedin FIG. 7), while the occurrence rate of a ghost image is tentativelyset to C=0.2.

TABLE 4 Divided Optical Divided Element F_(β) Optical Optical DisposedPoint- Regions Element F_(α) Symmetrically s_(α) s_(β) Mx(F_(α), F_(β))AF₁ F₁ F₂ 100 80 0.16 AF₂ F₂ F₁ 80 100 0.25 AF₃ F₃ F₄ 60 40 0.13 AF₄ F₄F₃ 40 60 0.30 AF₅ F₅ F₆ 30 20 0.13 AF₆ F₆ F₅ 20 30 0.30 Sum of Squaresof Mx(F_(α), F_(β)) 0.30

If the images from all the divided optical elements are to be usedequally in analyzing the object, an influence of the ghost image on theaccuracy of the analytical value of the object can be estimated by avalue obtained by squaring the mixing rate Mx(F_(β),F_(α)) of a ghostimage corresponding to each of the divided optical elements and addingthe squares. The value obtained by calculating the sum of squares is0.30.

Meanwhile, Table 5 indicates a result for the conventional comparativeexample, obtained through a similar calculation.

TABLE 5 Divided Optical Divided Element F_(β) Optical Optical DisposedPoint- Regions Element F_(α) Symmetrically s_(α) s_(β) Mx(F_(α), F_(β))AF₁ F₁ F₆ 100 20 0.04 AF₂ F₂ F₅ 80 30 0.08 AF₃ F₃ F₄ 60 40 0.13 AF₄ F₄F₃ 40 60 0.30 AF₅ F₅ F₂ 30 80 0.53 AF₆ F₆ F₁ 20 100 1.00 Sum of Squaresof Mx(F_(α), F_(β)) 1.40

In the comparative example, the sum of squares is 1.40, which is 4.7times greater than the sum of squares of the mixing rate according tothe present embodiment. Therefore, with the arrangement of the dividedoptical elements and the optical regions described in the presentembodiment, an influence of the mixing of a ghost image can be reducedas compared with the comparative example, and consequently it ispossible to say that the accuracy of the analytical value of the objectcan be increased.

The point of the present embodiment lies in that the divided opticalelement and the optical region corresponding to an image with thehighest mean luminance and the divided optical element and the opticalregion corresponding to an image with the lowest mean luminance aredisposed so as not to be point-symmetric with respect to the opticalaxis.

A reason why such an arrangement is preferable will be describedqualitatively. When a ghost image with the highest mean luminance ismixed into a normal image with the lowest mean luminance, the mixingrate is maximized, and an error of analysis occurring when thecharacteristics of the object are analyzed from that image alsoincreases. Meanwhile, even when a ghost image with a relatively highmean luminance is mixed into a normal image with a high mean luminance,the mixing rate does not become high. Thus, an error occurring when thecharacteristics of the object are analyzed from that image is likely tofall within a permissible range.

In addition, when the feature of the present embodiment is furthergeneralized, it can be said that two optical regions (two types ofdivided optical elements) in which light rays are incident on pixelsfrom which images with a large difference in the mean luminance areobtained are disposed so as not to be point-symmetric with respect tothe optical axis V₀. When this feature is viewed from anotherperspective, it can also be said that two optical regions (two types ofdivided optical elements) in which light rays are incident on pixelsfrom which images with close mean luminances are obtained are disposedso as to be point-symmetric with respect to the optical axis V₀. Thatis, when the two optical regions (two types of divided optical elements)corresponding to the images with a large difference in the meanluminance are disposed so as not to be point-symmetric with respect tothe optical axis V₀, the two optical regions (divided optical elements)corresponding to the images with close mean luminances are disposed soas to be point-symmetric with respect to the optical axis V₀, as aresult.

Therefore, when there are six regions as in the present embodiment,modes of the arrangement of the divided optical elements F₁ through F₆and the optical regions AF₁ through AF₆, which are disposed so as to bepoint-symmetric with respect to the optical axis V₀, are as follows. Thearrangement illustrated in FIG. 7 satisfies all of these conditions.

(1) F₁ and F₆ (AF₁ and AF₆) are disposed so as not to be point-symmetricwith respect to the optical axis V₀.

(2) F₁ and F₂ (AF₁ and AF₂) may be disposed so as to be point-symmetricwith respect to the optical axis V₀.

(3) F₅ and F₆ (AF₅ and AF₆) may be disposed so as to be point-symmetricwith respect to the optical axis V₀.

Another mode in the present embodiment is that the divided opticalelements F₁ and F₆ (i.e., the optical regions AF₁ and AF₆) are disposedso as not to be adjacent to each other. A reason therefor is that partof light that has passed through a given region is incident, as acrosstalk component, on pixels corresponding to an adjacent region. Ifthe divided optical elements F₁ and F₆ are adjacent to each other, partof the light that has passed through F₁ is incident on the pixels f₆corresponding to F₆. An image corresponding to F₆ has the lowest meanluminance, and an image corresponding to F₁ has the highest meanluminance. Therefore, an influence of crosstalk on the imagecorresponding to f₆ is maximized, and the accuracy of the analyticalvalue of the object decreases. Accordingly, the divided optical elementsF₁ and F₆ may be disposed so as not to be adjacent to each other. It isto be noted that, in the arrangement of the divided optical elementsillustrated in FIG. 7, F₁ and F₆ are disposed so as not to be adjacentto each other.

As described thus far, according to the embodiment of the presentdisclosure, the divided optical element corresponding to an image withthe highest mean luminance and the divided optical element correspondingto an image with the lowest mean luminance are disposed so as not to bepoint-symmetric with respect to the optical axis V₀. This configurationmakes it possible to suppress an influence of a ghost image, and anaccurate analytical value of an object can thus be obtained.

Second Embodiment

Although the arrangement of the divided optical elements in a case inwhich the areas of the regions are equal to one another has beendescribed in the first embodiment above, the areas may differ among theregions. For example, in a region A illustrated in FIG. 9, the areas ofA₃ and A₄ are different from the areas of A₁, A₂, A₅, and A₆. When theareas of the divided regions differ, depending on where a dividedoptical element is disposed, the mean luminance of an imagecorresponding to that divided optical element varies. A method fordetermining an arrangement of divided optical elements in such a casewill be described with reference to a flowchart illustrated in FIG. 10.

As in the first embodiment, six divided optical elements are representedby F_(a), F_(b) F_(c), F_(d), F_(e), and F_(f). In a disposing step1101, the divided optical elements F_(a) through F_(f) are disposed inthe region A in the imaging apparatus, as illustrated in FIG. 11.

In an imaging step 1102, a predetermined object is imaged by the imagingapparatus under a predetermined illumination condition, and images Q₁through Q₆ are obtained. In a calculation step 1103, portionscorresponding to the predetermined object are extracted from theobtained images Q₁ through Q₆, and the mean luminance of each portion iscalculated. In a numbering step 1104, the divided optical elements F_(a)through F_(f) corresponding to the calculated mean luminances arerearranged and numbered in descending order of the mean luminance. Up tothis point, the processes are similar to those of the first embodiment.

In a determination step 1105, it is determined whether the dividedoptical elements F₁ and F₆ are disposed so as to be point-symmetric withrespect to the optical axis V₀. If the divided optical elements F₁ andF₆ are disposed so as to be point-symmetric, in a rearrangement step1106, the divided optical elements F_(a) through F_(f) are rearranged inthe regions A₁ through A₆ in a pattern different from the previouspattern. Thereafter, the imaging step 1102 through the determinationstep 1105 are repeated. The process is terminated when the dividedoptical element F₁ and the divided optical element F₆ are disposed so asnot to be point-symmetric.

Although the number of regions in the embodiments described above issix, the number of regions may be other than six as long as a dividedoptical element corresponding to an image with the highest meanluminance and another divided optical element corresponding to an imagewith the lowest mean luminance can be disposed so as not to bepoint-symmetric. In a case in which a divided optical elementcorresponding to an image with the highest mean luminance and anotherdivided optical element corresponding to an image with the lowest meanluminance are disposed so as not to be point-symmetric with respect tothe optical axis V₀ and so as not to be adjacent to each other in orderto prevent an influence of a crosstalk component as described above, thenumber of regions may be six or more. As another embodiment in which thenumber of regions is six or more, an example of the arrangement ofdivided optical elements and optical regions when the number of regionsis eight is illustrated in FIG. 12A. In addition, examples of thearrangements of divided optical elements and optical regions when thenumber of regions is nine are illustrated in FIGS. 12B and 12C.

An arrangement of divided optical elements in a case in which the numberof regions is n and the divided optical elements are numbered as F₁, F₂,. . . , F_(n) in order of the mean luminances is generalized as follows.

(1) F₁ and F_(n) (AF₁ and AF_(n)) are disposed so as not to bepoint-symmetric with respect to the optical axis V₀.

(2) F₁ and F₂ (AF₁ and AF₂) may be disposed so as to be point-symmetricwith respect to the optical axis V₀.

(3) F_(n−1) and F_(n) (AF_(n−1) and AF_(n)) may be disposed so as to bepoint-symmetric with respect to the optical axis V₀.

Alternatively, the number of regions may be five. In this case, it isnot possible to dispose the divided optical element F₁ and the dividedoptical element F_(n) so as not to be point-symmetric with respect tothe optical axis V₀ and so as not to be adjacent to each other, and thusdisposing the divided optical element F₁ and the divided optical elementF_(n) so as not to be point-symmetric takes a priority, as illustratedin FIG. 13B. Here, at least two of the sensitivities of the image sensorto light rays that have passed through the respective divided opticalelements may be different from each other. Alternatively, as illustratedin FIG. 13B, at least two of the areas of the respective regions may bedifferent from each other. For example, in FIG. 13B, the area of theregion corresponding to F₃ is different from the areas of the otherregions. In any case, an effect of suppressing an influence of a ghostimage and obtaining an accurate analytical value of an object can beachieved. As another alternative, as illustrated in FIG. 13A, the numberof regions may be four, and at least two of the areas of the respectiveregions may be different from each other. For example, in FIG. 13A, thearea of the region corresponding to F₃ is different from the areas ofthe other regions. Furthermore, at least two of the sensitivities of theimage sensor to light rays that have passed through the respectivedivided optical elements may be different from each other. In this caseas well, an effect of suppressing an influence of a ghost image andobtaining an accurate analytical value of an object can be achieved.

In addition, although the mean luminances of the images corresponding tothe six optical regions are mutually different in the first embodimentdescribed above, as long as there are at least three different meanluminances, it is possible to dispose an optical region (divided opticalelement) in which a light ray is incident on pixels from which an imagewith the highest mean luminance is obtained and another optical region(divided optical element) in which a light ray is incident on pixelsfrom which an image with the lowest mean luminance is obtained so as notto be point-symmetric. Through this configuration, an effect ofsuppressing an influence of a ghost image and obtaining an accurateanalytical value of an object can be achieved.

Although the method for determining an arrangement of the dividedoptical elements F₁ through F₆ on the basis of the mean luminances s₁,s₂, . . . , and s₆ of the images obtained by imaging the predeterminedobject under the predetermined illumination condition has been describedin the embodiment above, another method that allows mean luminances ofimages to be estimated may be used. For example, the transmittance of adivided optical element under the predetermined illumination conditionis represented by T; the area of a region corresponding to the dividedoptical element is represented by D; and the sensitivity of the imagesensor to the light that has passed through the divided optical elementis represented by R. In this case, the mean luminance of the image isconsidered to be proportional to T×D×R. Therefore, if the spectralcharacteristics of the illumination, the transmission characteristics ofthe divided optical element, the area of the region, and the spectralsensitivity characteristics of the image sensor are known, thearrangement of the divided optical elements can be determined withoutthe mean luminances of the images actually measured.

Furthermore, when the spectral transmittance characteristics of all thedivided optical elements have the same profile (the absolute values ofthe transmittances may differ), it becomes unnecessary to take intoconsideration the spectral characteristics of the illumination and thespectral sensitivity characteristics of the image sensor. In this case,if the transmission characteristics of the divided optical element andthe area of the region are known, the arrangement of the divided opticalelements can be determined without the mean luminances of the imagesactually measured.

In addition, in a case in which the areas of all the regions are equal,if only the transmission characteristics of the divided optical elementare known, the arrangement of the divided optical elements can bedetermined without the mean luminances of the images actually measured.

In addition, although a configuration for obtaining the images Q₁through Q₆ corresponding to the respective divided optical elements hasbeen described in the embodiment illustrated in FIG. 1, the embodimentmay provide an analyzing apparatus that further includes a processorthat obtains an analytical value of an object on the basis of the imagesQ₁ through Q₆ of the object. This analyzing apparatus, for example, mayfurther include a memory that stores a relation between the luminance ofan image of the object and the analytical value of the object. Theprocessor may refer to the aforementioned relation stored in the memoryand obtain an analytical value of the object on the basis of theluminance of the image of the object obtained from the pixels. Theanalytical value, for example, may be an amount of a component includedin the object.

In addition, although the number of pixels included in N₁ (i.e., thenumber of pixels corresponding to a single micro-optical component M₁)is equal to the number of regions in the embodiment illustrated in FIG.3, the number of pixels included in N₁ may be greater than the number ofregions.

In addition, the center of the transmission wavelength band of theband-pass filter in the present embodiment may lie in a range from 700nm to 1100 nm inclusive. In a typical image sensor, the sensitivityvaries greatly in this wavelength band, and thus the difference amongthe mean luminances of images corresponding to the respective dividedoptical elements (i.e., the band-pass filters) tends to increase.Therefore, by applying the arrangement of the divided optical elementsdescribed above, a particularly great effect of suppressing an influenceof a ghost image and obtaining an accurate analytical value of an objectcan be achieved.

In addition, the configurations of the imaging apparatus and theanalyzing apparatus described in the embodiments above are not limitedto the configurations described above, and various modifications can bemade.

The imaging apparatus disclosed in the present disclosure can be usedeffectively as an imaging apparatus in a digital still camera, a videocamera, an in-vehicle camera, a security camera, and so on. In addition,the analyzing apparatus of the present disclosure can be applied to amedical, aesthetic, food, or chemical analysis or the like.

What is claimed is:
 1. An imaging apparatus, comprising: a lens opticalsystem including a lens, a stop, and an optical element including firstthrough nth divided optical elements and having first through nthoptical regions, n being an integer equal to or greater than five, thefirst through nth optical regions being defined in the respective firstthrough nth divided optical elements along a plane perpendicular to anoptical axis and positioned to be point-symmetric with respect to theoptical axis; an image sensor on which light that has passed through thefirst through nth optical regions is incident, the image sensorincluding first through nth pixels; and a microlens array disposedbetween the lens optical system and the image sensor, the microlensarray guiding the light that has passed through the first through nthoptical regions to the first through nth pixels, respectively, whereinmean luminances of images obtained from the first through nth pixelswhen a predetermined object is imaged under a predetermined illuminationcondition by using the lens optical system, the image sensor, and themicrolens array are represented by s₁, s₂, . . . , and s_(n),respectively, at least three of s₁, s₂, . . . , and s_(n) are mutuallydifferent values, a relation of s_(i)≧s_(i+1) is satisfied for any ithat satisfies 1≦i≦n−1, and the first optical region and the nth opticalregion are positioned not to be point-symmetric to each other withrespect to the optical axis.
 2. The imaging apparatus according to claim1, wherein at least two of areas of the first through nth opticalregions are different from each other.
 3. The imaging apparatusaccording to claim 2, wherein at least two of sensitivities in the firstthrough nth pixels when the light that has passed through the firstthrough nth optical regions are incident on the first through nth pixelsare different from each other.
 4. The imaging apparatus according toclaim 1, wherein the predetermined object is a white reflectancestandard.
 5. The imaging apparatus according to claim 1, wherein the(n−1)th optical region and the nth optical region are positioned to bepoint-symmetric to each other with respect to the optical axis.
 6. Theimaging apparatus according to claim 1, wherein the first optical regionand the second optical region are positioned to be point-symmetric toeach other with respect to the optical axis.
 7. The imaging apparatusaccording to claim 1, wherein the first optical region and the nthoptical region are not adjacent to each other.
 8. The imaging apparatusaccording to claim 1, wherein the predetermined illumination conditionis a condition in which light is emitted from a halogen lamp.
 9. Theimaging apparatus according to claim 1, wherein at least one of thefirst through nth divided optical elements is a band-pass filter. 10.The imaging apparatus according to claim 9, wherein a center of atransmission wavelength band of the band-pass filter lies in a rangefrom 700 nm to 1100 nm inclusive.
 11. The imaging apparatus according toclaim 1, wherein at least one of the first through nth divided opticalelements is a polarization filter.
 12. The imaging apparatus accordingto claim 1, wherein at least one of the first through nth dividedoptical elements is a neutral density filter.
 13. An analyzingapparatus, comprising: an imaging apparatus, including a lens opticalsystem including a lens, a stop, and an optical element including firstthrough nth divided optical elements and having first through nthoptical regions, n being an integer equal to or greater than five, thefirst through nth optical regions being defined in the respective firstthrough nth divided optical elements along a plane perpendicular to anoptical axis and positioned to be point-symmetric with respect to theoptical axis, an image sensor on which light that has passed through thefirst through nth optical regions is incident, the image sensorincluding first through nth pixels, and a microlens array disposedbetween the lens optical system and the image sensor, the microlensarray guiding the light that has passed through the first through nthoptical regions to the first through nth pixels, respectively, whereinmean luminances of images obtained from the first through nth pixelswhen a predetermined object is imaged under a predetermined illuminationcondition by using the lens optical system, the image sensor, and themicrolens array are represented by s₁, s₂, . . . , and s_(n), at leastthree of s₁, s₂, . . . , and s_(n) are mutually different values, arelation of s_(i)≧s_(i+1) is satisfied for any i that satisfies 1≦i≦n−1,and the first optical region and the nth optical region are positionednot to be point-symmetric to each other with respect to the opticalaxis; and a processor adapted to obtain an analytical value of theobject on the basis of images of the object that are obtained from thefirst through nth pixels.
 14. An imaging apparatus, comprising: a lensoptical system including a lens, a stop, and an optical elementincluding first through nth divided optical elements and having firstthrough nth optical regions, n being an integer equal to or greater thanfive, the first through nth optical regions being defined in therespective first through nth divided optical elements along a planeperpendicular to an optical axis and positioned to be point-symmetricwith respect to the optical axis; an image sensor on which light thathas passed through the first through nth optical regions is incident,the image sensor including first through nth pixels; and a microlensarray disposed between the lens optical system and the image sensor, themicrolens array guiding the light that has passed through the firstthrough nth optical regions to the first through nth pixels,respectively, wherein areas of the first through nth optical regions arerepresented by D₁, D₂, . . . , and D_(n), respectively, transmittancesof the first through nth optical regions under a predeterminedillumination condition are represented by T₁, T₂, . . . , and T_(n),respectively, sensitivities in the first through nth pixels when thelight that has passed through the first through nth optical regions areincident on the first through nth pixels are represented by R₁, R₂, . .. , and R_(n), respectively, andB _(m) =D _(m) ×T _(m) ×R _(m)(m=1 through n), at least three of B₁, B₂,. . . , and B_(n) are mutually different values, a relation ofB_(i)≧B_(i+1) is satisfied for any i that satisfies 1≦i≦n−1, and thefirst optical region and the nth optical region are positioned not to bepoint-symmetric to each other with respect to the optical axis.
 15. Theimaging apparatus according to claim 14, wherein at least two of areasof the first through nth optical regions are different from each other.16. The imaging apparatus according to claim 15, wherein at least two ofR₁, R₂, R₃, and R₄ are different from each other.